System, device and method for levelling floors

ABSTRACT

The present invention relates to a system, a device and a method for leveling floor surfaces by means of a floor grinding machine ( 10 ), in which the device comprises a lifting device ( 90 ) for adjusting the height of the floor grinding machine above the floor surface during leveling thereof. The system for leveling floor surfaces by means of the floor grinding machine comprises a laser transmitter ( 60 ) which is operatively connected to at least one laser receiver ( 61 ), which is arranged on the sensing device ( 70 ), and the method for leveling floor surfaces by means of the floor grinding machine is performed in that the laser transmitter ( 60 ) emits a signal which is received by a laser receiver ( 61 ), which is arranged on the sensing device ( 70 ) and the height of which is thereby detected and converted into a possible deviation in the level of the floor surface, the height of the floor grinding machine and hence the removal of the floor surface being adjusted in relation to this possible deviation in the level during leveling of the floor surface.

TECHNICAL FIELD

The present invention relates to a system, a device and a method forleveling floors by grinding.

STATE OF THE ART

Machines and tools for grinding floors composed of stone, such asnatural stone, concrete and wood are currently available. The buildingindustry currently employs techniques in which the building is producedin factories in the form of multiple different modules. The building ismerely assembled on a concrete slab on the site where it is to stand.This system requires an extremely level concrete base with ±1 mmdifference in height between the highest and the lowest point. Nomachines currently on the market are capable of achieving this withoutrepeated manual measurements and gradual intermediate grinding.

The building industry also employs building techniques which requireeven more level concrete bases, especially for high-rise storage inwhich automatically raising and lowering trucks move and lift palletsetc. up to great heights and down whilst simultaneously transportingthem by means of a vehicle moving along the concrete floor. Thisrequires very precise tolerances for the levelness of the floor, in thatthe pallet may be situated several meters, possibly tens of meters up inthe air whilst being moved vertically and laterally, and minor anomaliesin the levelness of the floor result in a very large deviation at thisheight and these fine tolerances cannot be achieved without machining ofthe concrete, which is both time-consuming and labor-intensive. Currenttechniques involve, among other things, grinding two tracks in thefloor, in and along which the truck moves, the tracks having to beextremely level. These tracks, however, make it harder to use the floorin that any vehicle passing over these tracks is disturbed by jolts andvibrations and can even become stuck in these and become harder tosteer.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a system, a device anda method for leveling floors by grinding, the height of the floor beingcontinuously measured and the rate of removal of a floor grinding devicebeing continuously controlled during leveling of the floor.

The present invention relates to a device for leveling floor surfaces bymeans of a floor grinding machine, which comprises a lifting device foradjusting the height of the floor grinding machine above the floorsurface during leveling thereof. The device comprises a sensing device,which is in contact with the floor surface during leveling of the floorand is connected to the floor grinding machine in such a way that thesensing device is afforded freedom to move basically perpendicular tothe floor surface that is to be leveled.

One embodiment according to the invention relates to a device in whichthe freedom of movement of the sensing device in a vertical direction isachieved by means of at least one slide rail, which basically extendsperpendicularly to the floor surface that is to be leveled.

Another embodiment of the invention relates to a device in which thesensing device comprises a stand, which is displaceable along the sliderail and which has a first free, lower end in contact with the floorsurface via a contact member during leveling thereof.

Yet another embodiment relates to a device in which the lifting devicecomprises a support wheel, which is height-adjustably connected to thefloor grinding machine via at least one moveable strut suspension.

A further embodiment relates to a device in which the strut is aparallel strut.

Yet another embodiment relates to a device in which the contact memberis at least one spherical roller and in a further embodiment the contactmember is at least one PCD dome.

A further embodiment relates to a device in which at least one laserreceiver is arranged on the sensing device and yet another embodimentrelates to a device in which a laser receiver is arranged at a secondfree, upper end of the stand.

The present invention also relates to a system for leveling floorsurfaces by means of a floor grinding machine, in which a lasertransmitter is operatively connected to at least one laser receiver,which is arranged on the sensing device.

The present invention further relates to a method for leveling floorsurfaces by means of the floor grinding machine, in which a lasertransmitter emits a signal which is received by a laser receiver, whichis arranged on the sensing device according to any of the precedingclaims and the height of which is thereby detected and converted into apossible deviation in the level of the floor surface, the height of thefloor grinding machine being adjusted in relation to this possibledeviation in the level during leveling of the floor surface.

According to the invention the height is measured by a rotational laserand a laser receiver on the grinding machine, the receiver being seatedon a sensing device in contact with the surface that is to be ground andthe sensing device being connected to the grinding machine via a slideattachment, which affords the sensing device a substantially verticalfreedom of movement in relation to the grinding machine and also thesupport wheel. The height deviation is registered and the machining ofthe concrete surface is regulated by a system which controls the liftingdevice. At the front edge of the grinding machine the lifting device isconnected to the wheel, which supports the grinding machine, saidlifting device in turn regulating the removal cut of the grindingmachine by raising, lowering or maintaining the height of the grindingmachine in relation to the surface that is to be ground and the supportwheel.

By means of the invention, which continuously measures the height andcontrols the machine accordingly, the floor leveling process is renderedconsiderably more efficient and greater levelness is achieved in floorgrinding, the grinding process also being rationalized. The inventionprovides a well-functioning floor leveling system, which affords greatlevelness in grinding. The invention reduces the number of personnelrequired and much of the time-consuming measurements, especially themanual measurements, and reduces the costs of floor leveling and thetime spent doing this. The object of the invention was to provide a newmeasuring system which was lacking on the market. The ambitions were todevelop an already existing floor grinding machine to also encompass ameasuring system. The results of the grinding tests show that themeasuring system according to the invention works. The points which wereraised too high in the measurement prior to grinding were machined andthe points that were too low were not machined. Since measurement isperformed at the front edge of the grinding head, certain low points aremachined by the rear edge of the grinding head where large differencesin level occur within a short space. There are several advantages withthe system according to the invention in that it is easy to move andassemble, and it saves time as a result of the smaller number ofmeasurements and also improves the accuracy, that is to say thelevelness after grinding. The design construction and the methodaccording to the invention are of great benefit to the operator whenhigh-precision grinding is required, and also afford economic advantagesdue to the low material costs. This means that the use of rotationallasers in producing a level grinding result is a good solution to theproblem and gives a more even result. The use of rotational lasers andat least one laser receiver provides a solution which fulfills theaccuracy requirement, which is robust and which is reasonably priced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail below with reference tothe drawings attached, in which

FIG. 1 shows an example of a grinding machine,

FIG. 2 shows an example of a grinding tool holder of the grindingmachine in FIG. 1,

FIG. 3 shows an example of a measuring device which can be used on thegrinding machine according to the invention,

FIG. 4 shows how an angular adjustment produces a vertical adjustmentaccording to the invention,

FIG. 5 shows the height adjustment according to FIG. 4 in more detail,

FIG. 6 shows the range and sensitivity for a receiver which can be usedin the measuring device according to the invention,

FIG. 7 shows an example of a receiver which can be used according theinvention,

FIG. 8 shows a side view of an embodiment of a lifting/measuring deviceaccording to the invention,

FIGS. 9 and 10 show perspective views of the lifting/measuring device inFIG. 8 from different angles,

FIG. 11 shows a side view of another embodiment of the lifting/measuringdevice,

FIG. 12 shows another part of the lifting/measuring device in FIG. 11,

FIG. 13 shows a part of FIG. 12 in greater detail,

FIG. 14 shows a part of the method for controlling the grinding machineaccording to the invention,

FIG. 15 shows another part of the method for controlling the grindingmachine according to the invention,

FIG. 16 shows yet another part of the method for controlling thegrinding machine according to the invention,

FIG. 17 shows a further part of the method for controlling the grindingmachine according to the invention,

FIG. 18 shows a floor measurement prior to grinding,

FIG. 19 shows a floor measurement after grinding,

FIG. 20 shows a flow chart for the method of controlling the grindingmachine according to the invention,

FIG. 21 shows a circuit diagram of the electrical design according tothe invention, and

FIG. 22 shows the measuring result from a test of the invention(surveying of concrete slab Strandgatan; difference from theoretical;+=raised slab; unit mm and scale 1:75).

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention relates to a system, a control system, a deviceand a method for leveling floors by means of grinding. The control andmeasuring system according to the invention is designed for a grindingmachine 10 (FIG. 1), which is radio-controlled in order to make the workeasier for the operator and is controlled via two brushless DCservomotors, each fitted to a wheel 20. The machine rests on these twowheels 20 and on one or more grinding disks 30 (FIG. 4). The dynamicfriction is considerably lower than the static friction, which meansthat in operation the machine becomes relatively easy to maneuver,despite its weight of 600 kg.

The motor that drives the grinding disks 30 is a three-phaseasynchronous motor 31 having a power output of 15 kW. The motor iscontrolled via a frequency converter, which feeds with a frequency of30-90 Hz, a belt drive system with gearing delivering a speed of 450 to1350 rpm. The grinding is performed by diamond tools, which are fixed tofour tool holders 40 mounted on the larger rotary grinding disk 30. FIG.2 shows one of the tool holders 40 with six tools 50. The tools are easyto change and the operator has the facility for choosing whether to useone, two, three or six tools, depending on the type of floor and thedesired rate of removal. The grinding machine 10 is also equipped with a“mist cooler system”, which means that a fine water mist is sprayed ontothe floor, which then cools the diamond tools 50. This results in moreefficient grinding and a longer tool service life.

The rotational laser 60 (FIG. 3) is a rotating laser levelinginstrument, which together with at least one or more laser receivers 61,for example two or three, measures the difference in height. Onefunction which most rotational lasers have is self-leveling and thispermits automatic self-leveling when it is activated. This functionallows an inclination of the laser of up to ±10 degrees withoutaffecting the accuracy. Another function is automatic level monitoring,which gives an alarm if the stand 70 should begin to drop or if theinstrument is dislodged from its original position. The rotational laserhas a robust design and the rotor head is protected by a laser housingenclosure, which can withstand a fall from a height of 1 meter onto aconcrete surface. It is also dust- and watertight, which permits use outof doors. The rotational lasers 60 used are of laser class 1, 2, 3A or3R, class 3A and 3R allowing a power output or pulse energy five timesgreater than class 2, although, when the beam is propagated by means ofan optical system, it becomes equivalent to class 2 from the riskstandpoint.

The laser receiver 61 (FIG. 7) is the unit which receives the signalemitted by the rotational laser 60 and accordingly indicates at whatheight the receiver is situated. The accuracy of the receiver 61 istaken into account, since it may vary from ±0.05 mm to ±12 mm, dependingon which unit is selected. Something else which should be considered isthe reception angle of the unit, which can also vary greatly from ±45degrees to 360 degrees. The receiver 61 is described in more detailbelow.

In order to create the measuring system, the rotational laser 60 isarranged on a stand on the fringes of the surface that is to bemachined, due to the fact that the rotational laser must not be affectedso that it is shifted out of its position. The receiver 61 that is usedto receive the laser signal is placed on the grinding machine 10 on topof the stand 70 as shown in FIGS. 8-10 and 11.

The placing of the laser receiver 61 has a great bearing on the accuracyof the measurement. Since the machine 10 is constantly in motion and theconditions change during the course of the machining, certain factorsneed to be considered when placing the receiver 61.

-   -   Tool wear—Tool wear affects the height of the machine in        relation to the floor. The difference between a brand new tool        and a worn-out tool may be up to 15 mm.    -   Same distance from the underlying surface—One requirement for        accuracy in the measurements is that the receiver 61 should        always be at a specific distance from the floor. This is in        order to afford the facility for assessing the levelness of the        floor through measurements of the difference in height in        relation to a reference point.    -   Thermal interference from the underlying surface—According to        Gunilla Blomkvist of NCC Construction Sverige AB, who was        measurements engineer on the construction of a concrete slab,        the measuring point relative to the floor plays a significant        role. The measuring point should be located half a meter above        the ground surface in order to avoid the effects of heat        radiated from the underlying surface. This is especially true of        laser measurement and the influence is most pronounced in warm        environments and especially on asphalt, although concrete also        gives off heat which could cause interference.    -   Vibrations—During grinding, vibrations occur in the machine 10.        The vibrations vary depending on factors such as the type of        tool 50, the grinding speed and material to be machined.        Observing the machine during the ongoing grinding process,        relatively small vibrations will be noted, which are assumed not        to cause problems with the measurements.

For these reasons, placing the sensor on existing parts of the machine10 is excluded without compensating for tool wear. This is because themachine rests with most of its weight on the grinding head and the restof the construction follows as the tool is worn, so that the grindinghead is always pressed against the floor. The result is that the machinewith grinding head and motor subsides as the tool wear progresses andvaries by 15 mm in a vertical direction depending on the state of thetool.

A separate sensing device 70 in the form of a receiver stand with areference wheel/ball or wearing surface against the floor, fixed to thefront edge of the grinding machine 10, results in an accuratemeasurement of the surface to be ground. The difference between new andworn tools results in a change in the angle, which leads to a variationin the distance between the surface and the receiver 61. This angularvariation can be calculated, making it possible to also calculate thevertical error. The receiver stand 70 is located in front of the machine10 (FIG. 8-10). The tool wear is 15 mm after half the length and isequal to 30 mm after the full length, as can be seen in FIG. 4.

The angular variation to which the tool wear gives rise affects thefront part of the machine 10 with the same angle as the change in thewheel axis. This angle gives rise to a variation in the verticaldirection, as shown in FIG. 5. The height of the measuring stand 70 is500 mm in this embodiment, but it may be shorter or longer in otherembodiments, in order to avoid the problem of heat radiation asdescribed earlier. The designation X in FIG. 5 is the new heightrelative to the ground/the floor.

Through calculations with various trigonometric correlations, it ispossible to calculate x and the variation in the vertical direction canbe written as

X ₁=500−X=500*(1−cos(α))

which gives the result

X ₁=500*(1−cos(1.3429))=0.1386 mm

The vertical error that occurs from new tools to completely worn-outtools is relatively small and is assumed not to cause major errors inthe accuracy of the system. Bearing in mind the problems described here,the measuring stand 70 which is located at the front edge of the machineis a good solution.

No receiver with signal pickup on the market meets the accuracyrequirements sought. The receivers which afford the facility forderiving useable signals are machine receivers designed to sit onexcavators, road graders or similar machines having a lesser accuracyrequirement. These receivers have an accuracy of about 10 mm and are notacceptable for this application. Receivers affording sufficiently highaccuracy are so-called handheld receivers 61. These have no facility fordelivering a useable electrical signal since the measuring result isonly displayed on an LCD screen and light-emitting diodes on thereceiver, giving an indication of the position of the receiver inrelation to the laser.

The handheld receivers 61 have an inclined surface with photodiodeswhere the laser strikes. The receiver 61 then has various ranges withinwhich the laser is deemed to lie. These ranges are illustrated in FIG.6. Since the receiver 61 has a sensitive range for zero level and thenext area is large, it will only be possible to use indications of howthe receiver lies in relation to the laser 60. This comes down to threesignals: High, Normal and Low. None of the manufacturers is willing todivulge information on how their product is designed or will come upwith proposals as to how signals can easily be coupled out. Withessentially only three signals it was decided to use the existinglight-emitting diodes 62 on the receiver 61, as can be seen from FIG. 7.

The receiver 61 causes both of the diodes 62 to light if the receiver issituated on a level with the laser 60 and only one of the diodes if itis too high or too low. The solution that was chosen for handling theexisting signals from the light-emitting diodes was phototransistors.The advantage to this is that the signals can be utilized without theneed to intervene in the receiver 61. With the measuring systemaccording to the invention, the machine 10 is controlled according tothe signals emitted by the receiver.

In order to produce a control system according to the invention, inwhich the result of the measurements is interpreted and the informationis then used to decide whether the floor needs to be machined, it isnecessary to control the rate of removal of the grinding machine 10. Thegrinding machine is equipped with a system in which the operator has thefacility for varying the rate of removal by adjusting the grindingspeed, the rate of advance or a change in the grinding pressure, whichis done manually by means of adjustable weights on the side of themachine.

A variation in the grinding speed by adjusting the rotational speed ofthe tools is a complex operation. The highest speed does not always givethe fastest removal, there being many other factors that come into playsuch as the tool used, what material is being ground and the moisturecontent of the material. The fact that the rate of removal is notproportional to the grinding speed is not the only problem to which anadjustment of the grind speed gives rise. Problems occur since thedesign of the machine is based on the fact that the dynamic friction islower than the static friction and adjusting the grinding speed givesrise to different prerequisites for the rate of advance.

The normal rate of advance during grinding is 0.2 m/s. This speed can beadjusted in order to increase the floor machining time and in this wayto increase the removal by a relatively simple intervention.

The signals that control the drive motors are 0-5 V, where 2,500 V isstationary. The signal could easily be connected to a PLC and damped ifremoval is to take place and could bypass the PLC without manipulationfor more rapid advance when removal is not to take place. One problemwith this is that it interferes with the operator's scope to drive thefloor grinding machine as he or she sees fit.

Another method for regulating the rate of removal is to adjust thegrinding pressure. This method is currently used partly by changing theadjustable weights and by placing external weights on the machine 10 inorder to increase the grinding pressure. This method can be applied inthat a lifting/elevating device lifts/elevates the machine 10 and inthis way removes large proportions of the weight of the machine andredistributes the weight to a support wheel 80, which is located at thefront edge of the machine. This would mean a reduced contact pressureagainst the floor and lead to slower removal.

The preferred method for regulating the rate of removal is a variationin the grinding pressure, involving a normal grinding pressure whenremoving material, which can then be reduced if an area does not need tobe machined. This affords a very simple facility for varying the rate ofremoval.

The grinding machine 10 (in this embodiment an HTC 950 RX model) has anaccessory in the form of a support/transport wheel 80, similar to thesupport wheels fitted to trailers. The floor grinding machine 10 thenrests on the two drive wheels 20 and the support wheel 80 fitted to thefront edge. This allows it to be moved, driven by the DC motors whichnormally steer the machine 10, or allows the machine to be rolledmanually, which would not be possible when the stationary tools are incontact with the floor.

The transport wheel 80 is the starting point for two embodimentsaccording to the invention. These can be seen from FIGS. 8 to 11. Thedevelopment of the transport wheel construction means that the systemaccording to the invention can easily be shifted to another machine 10.Parts of the existing support wheel construction are used to reducecosts and also to improve the compatibility with existing grindingmachines. In order not to create any problems in turning or in grinding,when the machine swivels in a sideways direction, the wheel 80 from theold construction is used. The major difference is that the manualelevation has been replaced by a lifting device 90 comprising anadjusting fixture 91. The function of the adjusting fixture is toelevate or lower the machine 10 and in this way to adjust the force withwhich the grinding head presses against the floor. The maximum capacityof the adjusting fixture 91 is 6800 N, which is sufficient for liftingthe entire weight of the machine.

The wheel 80 that is used requires that the suspension should always bevertical to the floor so that the height will not be affected by themodified wheel angle. This problem is solved in that the lifting device90 also comprises a load cell 92 for sensing what load the wheel 80 isbeing subjected to. FIGS. 11 and 12 show the fitted load cell 92 in afirst embodiment. Knowing the load on the wheel 80 via the load cell 92,it is possible to estimate the grinding pressure. The adjusting fixture91 adjusts the machine 10 to the given levels of grinding pressure,depending on the level of the surface. This results in a constant heightfrom the floor irrespective of the position of the wheel 80.

The system according to the invention is based on the fact thatmeasurements which give the level of the floor are performedcontinuously. In order to achieve this, the measuring stand 70 must havecontact with the underlying surface, that is to say the floor, and mustbe able to slide freely when attached to the grinding machine 10. Themeasuring stand 70 is designed with a contact member 73 in the form ofat least one spherical roller on the end/bottom or at least onepolycrystalline or compact diamond (PCD) dome (one embodiment in FIGS.11 and 12 has a PCD dome whilst a second embodiment in FIGS. 8-10 hastwo PCD domes as contact members and is arranged on a parallel strut 100in order to ensure that the wheel 80 is perpendicular to the floor),which touches the floor surface and allows movement in all directions.Since the measuring stand 70 only needs to carry its own weight, thespherical roller/PCD dome successfully copes with the load by a largemargin.

The fixing to the grinding machine 10 comprises two slide rails 71fitted to the stand 70 and attachments 72 to the modified support wheelconstruction and the parallel strut construction 100. The reason forusing two rails is that it lends greater stability in response tomovement in all horizontal directions. The construction according to theinvention allows the stand to move freely in a vertical direction andmeans that each spherical roller/PCD dome is at all times pressedagainst the underlying surface under the stand's own weight.

For the control system, a separate electrical switch box is used with afunction relay as central unit. A circuit diagram of the electricaldesign is shown in FIG. 21. Zelio Logic is a digital function relaymanufactured by Telemecanique, which is used in the control system. Thefunction relay is supplied with 24 V DC and is fitted on a 35 mm DINrail, which affords good prerequisites for fitting in the electricalswitch box. Zelio Logic has eight digital inputs for 24 V DC, of whichfour can be used for analog signals in the range 0-10 V. The internalA/D converter uses 8 bits, which gives an acceptable resolution. Theoutputs provided are four relay outputs which can cope with 8 A.

The load cell 92 (FIGS. 11-13) used in the invention is a TB model. Abending beam is used to measure pressure and is capable of measuring0-500 kg with a safe overload of 750 kg, which means that it can handlethe full weight of the machine 10. The maximum supply is 15 V DC and theoutput signal is 2 mV/V, which means a maximum output signal of 20 mV atfull load when the feed voltage is 10 V. Strain gauges are fitted insidea cavity in the load cell 92. Two gauges measure the longitudinalextension and two measure the transverse extension. The four straingauges are coupled to a Wheatstone bridge. The bridge connection to fourgauges means that the load cell 92 does not become sensitive to changesin resistance due to changes in temperature.

In the first embodiment as shown in FIGS. 8-10, the load cell 92 islocated so that it senses the force to which the adjusting fixture 90 issubjected. In the second embodiment according to FIGS. 11-13 the loadcell measures the pressure to which the wheel 80 is subjected, fromwhich the contact pressure of the grinding head can be calculated. Theseembodiments mean that through the load cell 92 it is possible to detectthe force which the grinding head of the grinding machine 10 is applyingto the underlying surface, that is to say the floor, allowing thesurface removal of the grinding machine to be automatically controlled.

In order to amplify the signal from the load cell 92, a load cellamplifier is used to convert signals from the load cell into an analogvoltage or current signal. The amplifier permits a connection from theload cell 92 to a PLC without the use of a separate balancinginstrument. The amplifier is adjusted by panel potentiometers mounted onthe front of the grinding machine 10.

The program used according to the invention has three signals. Two ofthese are discrete signals emanating from the phototransistors, whichare high when the light-emitting diodes 62 on the receiver 61 light up.The third input signal emanates from the load cell amplifier and is ananalog signal, which is converted by an 8-bit A/D converter. The twodiscrete input signals also go to timer circuits, which convert thesignals into pulses. This step makes it possible, by simple means, tohandle the signals generated by light-emitting diodes. This is followedby a processor step, in order to prevent the system reacting to just onemeasurement without availing itself of a mean value in assessing whetheror not the surface is to be ground. This step has four processors, whichcount pulses from each input, when both of the inputs are activesimultaneously, and the total number of pulses. FIG. 14 shows the timercircuits to which the inputs go and how the signals are relayed to theprocessor step.

After the processor step comes a comparator step (FIG. 15), which bymeans of ensuing gate logic interprets the information in the processorsand determines whether the surface is to be machined. The output signalfrom this step consists of a discrete signal, where high signifies thatthe surface is higher than the reference and is to be machined.

In order to provide a memory, which retains the information on whetherthe surface is to be machined, a processor is used. The memory functionsso that, if grinding is to be performed, the processor contains thedigit 0 and, if the surface is not to be machined, the processorcontains the digit zero. FIG. 16 shows the processor and the rest of thecircuits for memory processing. The information from the memory is usedto select what pressure the load cell 92 must bear. The signal from theload cell is compared with preprogrammed values for the various levels.The preprogrammed levels also contain tolerance limits so thatvibrations and other interference will have less influence. Depending onthe signal from the memory, the pressure on the load cell is adjusted,which means that machining of the surface is always performed with thesame pressure and the grinding head is always elevated by the sameheight when grinding is not to be performed. FIG. 17 shows thecomparators, which determine whether the pressure on the load cell 92 iswithin the correct levels. According to the comparators, the memorydetermines what signals are to be used and relayed to the outputs thatcontrol the adjusting fixture 91.

On construction sites, measurements are at present performed manually atintervals of approximately one meter and measurements are repeated manytimes with intervening grinding in order to meet the accuracyrequirements, which are often of ±1 mm. The measuring result from abuilding project is shown in FIG. 19. In order to simulate themeasurements performed outside on the building project, heightmeasurements were undertaken on the concrete slab within a rectangulararea measuring 3.5×1 m. On this area 24 measurements of the heightrelative to a reference point were undertaken, so that the measurementswere performed at intervals of half a meter. The DNA 03 instrument fromLeica was used for the measurements. This instrument is made forindustrial measurements and has a high accuracy with a standarddeviation of 0.3 mm per kilometer. FIG. 18 shows the levels measuredbefore grinding with all measurements given in tenths of a millimeter.All results from the measurements presented in this description are intenths of a millimeter and all measurements have the same fixedreference point, in order to provide an easy way of comparing theresults.

In order to get the surface level, an area larger than the actualmeasured area was machined. The measuring points on the short sides ledto complications as the grinding machine 10 could not get to machinethese points. This problem was due to the placing of the measuredsurface and where the grinding was performed the concrete base waspoured using two grades of concrete, one harder and one softer. In orderto locate the entire measuring surface on the same type of concrete, ithad to be applied in such a way that grinding of the outer points becameimpossible. For this reason the measuring result from the outermeasuring points on the upper short side should not be evaluated wheninterpreting the result.

The zero level for the measuring system, the level which the machine 10is intended to achieve, is set to 0.3 mm, which corresponds to the value3 in the drawings showing the result for the various measurements. Theresult measured after grinding is shown in FIG. 19. As the measurementsshow, an accuracy of ±2.2 mm was obtained. An error in the grindingmeant that the machine was stationary and machining the same point for alonger period of time, which is reflected in the result from the pointhaving the value −1. No great significance need be attached to thispoint.

Other embodiments of the invention with other equipment, such as abetter laser 60 or receiver 61, and the capacity to extract bettersignals with an indication of how much the level differs from thereference are conceivable. A laser 60 affording better accuracy togetherwith a receiver 61 with greater sensitivity affect the overall accuracy,giving a better result. With signals which more precisely describe thedeviation from the reference, it should be possible to achieve animproved adjustment of the grinding pressure. In another embodiment theconstruction can be modified so that the lifting device 90 is morestably fixed to the top in the second embodiment and not attached to theload cell 92, which is in turn anchored to the machine 10. In the firstembodiment with parallel strut 100, which anchors the wheel 80 morestably and with less dependence on the degree of inclination, theadjusting fixture 90 is arranged inside the strut 100.

Conceivable future embodiments may involve the use of a laser andreceiver affording better accuracy, which should give the system as awhole an improved accuracy. A receiver with good accuracy in which thedifference in level is expressed as an analog output signal shouldafford significantly better scope for more precise selection of asuitable grinding pressure. It would also be desirable for the receiverto be capable of receiving laser signals from all directions. Aspecially manufactured load cell 92 for detecting the grinding pressurecombined with a more stable construction of the lifting device 90 isexpected to afford a facility for more precise control of the grindinghead elevation in the second embodiment. The first embodiment is morestable. The measuring stand 70 can have a more stable attachment to theconstruction, in order to avoid changes in position and to counteractthe effects of vibrations, which occur during the grinding process. Thereceiver 61 can be fixed to the measuring stand 70 so that it cannot bedislodged from its position. In continued use of the embodiment with aspherical roller 73, a system should be designed which automaticallycleans the surface before the spherical roller passes over it. Onevariant for implementing this system is compressed air. The use ofembodiments with one, two or more PCD domes 73, however, eliminates theneed for cleaning, since there are then no moving parts to become fouledwith dirt. Some form of display should also be implemented in order toprovide the operator with information on the height compared to thereference point. This function would mean that the operator can steerthe machine 10 more towards the points in need of machining and canavoid going over the points that have attained the correct level, sincemachining does not occur at these points anyway.

Another feasible but currently too expensive embodiment of the measuringsystem involves the use of a laser tracker as used primarily fordetermining the coordinates of large objects in the aviation,shipbuilding and automotive industries, since this technique combinesboth laser interferometry and goniometry. This measuring system has anaccuracy of 0.1 mm at a distance of 100 meters, where measurement isperformed at a speed of up to 1000 points per second.

One method of controlling the leveling of the floor surface by means ofthe grinding machine 10 is shown in FIG. 20. This method is performed instages in that the rotational laser 60 emits a light signal, which isreceived by the receiver 61, the height of which is read off/detectedand converted in that the rotational laser (the laser receiver 61 alwaysbeing at a distance of x mm from the floor, see FIG. 5 and the distancex being set via adjustment of the receiver or raising/lowering of thelaser) lays out a plane in the space and the receiver 61 senses itsposition for any deviation relative to the floor plane by means ofsignals, which are processed by the control system according to theinvention (which forms a mean value from a number of points over a shortdistance) and, if the floor surface is too low in relation to thereference, the grinding pressure is reduced and, if the floor surface istoo raised, the grinding pressure is increased. The reference is theheight of the laser plane minus the length of the measuring stand 70 tothe zero position of the laser receiver 61. Calibration of the referencepoint for the laser transmitter 60 and the laser receiver 61, however,is not necessary. This means that the grinding pressure adjustment isperformed by imposing elements of the pressure from the grinding head onthe wheel 80 at the front edge of the machine. This gives a reducedgrinding pressure, so that the grinding pressure can be increased bywithdrawing the pressure from the front wheel 80, so that the weight ofthe entire machine again rests on/presses the grinding head down withthe grinding disk 30 and the grinding tools 50.

1. A device for leveling floor surfaces by means of a floor grindingmachine, which comprises a lifting device for adjusting the height ofthe floor grinding machine above the floor surface during levelingthereof, wherein a sensing device, which is in contact with the floorsurface during leveling of the floor surface, is connected to the floorgrinding machine in such a way that the sensing device is affordedfreedom to move basically perpendicular to the floor surface that is tobe leveled and senses the levelness of the floor for interaction withthe lifting device when adjusting the height of the floor grindingmachine above the floor surface according to the sensing.
 2. The deviceas claimed in claim 1, wherein the freedom of movement of the sensingdevice in a vertical direction is achieved by means of at least oneslide rail, which basically extends perpendicularly to the floor surfacethat is to be leveled.
 3. The device as claimed in claim 1, wherein thesensing device comprises a stand, which is displaceable along the sliderail and which has a first free, lower end in contact with the floorsurface via a contact member during leveling thereof.
 4. The device asclaimed in claim 1, wherein the lifting device comprises a supportwheel, which is height-adjustably connected to the floor grindingmachine via at least one moveable strut suspension.
 5. The device asclaimed in claim 4, wherein the strut is a parallel strut.
 6. The deviceas claimed in claim 3, wherein the contact member is at least onespherical roller.
 7. The device as claimed in claim 3, wherein thecontact member is at least one PCD dome.
 8. The device as claimed inclaim 1, wherein at least one laser receiver is arranged on the sensingdevice in such a way that the laser receiver is always at a specificdistance from the floor.
 9. The device as claimed in claim 3, wherein alaser receiver is arranged at a second, free upper end of the stand. 10.A system for leveling floor surfaces by means of a floor grindingmachine, wherein a laser transmitter is operatively connected to atleast one laser receiver, which is arranged on the sensing deviceaccording to any one of the preceding claims.
 11. A method for levelingfloor surfaces by means of a floor grinding machine, wherein a lasertransmitter emits a signal which is received by a laser receiver, whichis arranged on the sensing device according to any of the precedingclaims and the specific height of which above the floor is therebydetected and converted into a possible deviation in the level of thefloor surface, the height of the floor grinding machine being adjustedin relation to this possible deviation in the level during leveling ofthe floor surface by means of the lifting device according to any one ofthe preceding claims.